1. Field of the Invention
The invention relates to a method and a device for wireless communication by which a scan for access networks can be performed.
2. Description of the Related Art
This invention is related to a network in which a device for wireless communication may establish a connection to one or more access networks. Examples for such access networks are Wireless Local Area Networks (WLAN), wherein each network is identified by a Service Set IDentifier (SSID).
There are several reasons why a device might connect to a plurality of access networks. Namely, certain applications have needs for different kind of networks. For example, access networks may include a company network, hotspot provider (ISP (Internet Service Provider) & operator) networks and home WLAN networks. Different networks can provide different set of destination networks. Here a couple of examples:
From a company network, it is possible to reach intranet and Internet but it might not be possible to send mails via your person ISP account. From a WLAN home network, you might not be possible to use intranet services. Also, in technologies like UMA (Unlicensed Mobile Access) it might not be possible to carry data over UMA in all operators, so that also in this case it might be necessary to change an access network or to use additionally an alternative access network.
Furthermore, scanning for new access networks might be advantageous in order to get cheaper connection, better performing connection, or to find a current network for a particular service, as described above. Also technologies like location information using WLAN may use extensively scanning.
When connecting to WLAN networks, it is necessary to scan for surrounding WLAN networks to which a WLAN station (STA) may connect. The scanning procedure may be a passive scan, in which the WLAN station listens to beacons delivered from surrounding Access Points (AP), or an active scan, in which the WLAN station sends probe requests and waits for an answer.
Currently, most operating systems provide a basic WLAN API (Application Programming Interface) that allows applications do the scanning of the surrounding WLAN networks. Normally, the scanning is done so that an application triggers a scan request via the API to a corresponding subsystem, which then performs the scan operation. By having all the applications to perform separate scan logic, this can create a situation where the whole system is scanning just about all the times due to one-to-one mapping of all the scan requests.
For example, it is assumed that a WLAN station (e.g., a mobile device) has six applications that each have decided to scan the surrounding networks every two minutes. This situation can result in that the system initiates a scan every 20 seconds, which is very unnecessary in most cases. This has a very large effect on power-consumption. Namely, the situation that the device has to scan every 20 seconds will cause the average power-consumption to go up by 60 mW, which is almost ten times more than a normal basic phone idle power-consumption.
FIG. 3 illustrates about the effects of the scanning to stand-by time. In particular, FIG. 3 shows the WLAN scanning impact on power consumption, wherein a smart phone performing scanning in the passive mode is taken as an example. On the ordinate, the stand-by time is plotted in hours. On the abscissa, the number of scans per hour is plotted. Furthermore, in this example a scan for only one WLAN network, indicated by the SSID (Service Set IDentifier) is carried out.
As clearly derivable from FIG. 3, the stand-by time drastically reduces when the number of scans per hour is increased.
Hence, it is desirable to reduce the scanning operations.
Heretofore, some implementations prohibit a system to do scanning too often, and they are implementing this feature so that the system returns the old scan result if a certain threshold time has not been passed since the previous scan. For example, the Nokia Communicator 9500 does it this way. However, this makes application programming tricky as they do not know if the scan results are actually current or not. Also, this type of behaviour forces all the applications to have separate timers and they wake up separately the application engine processor thus increasing power-consumptions. Hence, this approach does not solve the problem sufficiently.
Furthermore, while a scan operation is performed, sending and receiving of data MPDUs (MAC (Medium Access Control) Protocol Data Unit) is not possible due to implementation limitation or it is very slow, so that the long time needed for the scan results affect applications, in particular applications that have real time requirements like voice. Thus, an increased number of scan operations may be annoying for the user of the WLAN station.